1. Field of the Invention
The present invention relates to the syringe devices, and more particular, to a syringe apparatus to which a pressure gauge is mounted for purposes of reading fluid pressures exerted within the barrel of the syringe.
2. The Prior Art
Syringes are used for many different kinds of medical applications. For example, when performing a coronary angioplasty a syringe apparatus is used to control injection of a contrast media through pressure tubing and through a lumen of a catheter to the distal end of the catheter where a balloon is inflated while positioned in a coronary artery in order to remove coronary artery blockage. Under these circumstances, the syringe must be capable of carefully controlling the injection of the contrast media under high pressures for carefully controlled durations of time. Accordingly, syringes have been devised which are equipped with a pressure gauge that is designed to monitor the pressure being exerted by the syringe on the contrast media as it is injected into the balloon that is located at the distal end of the catheter.
One of the most widely used types of pressure gauges used for this purpose is a simple standard strain gauge which is mounted on the barrel of the syringe. The strain gauge has a dial on the upper face of the gauge and a needle which is used to read pressures within a selected range. Commonly, the strain gauge is mounted to the syringe by the use of a threaded coupling. In other words, typically the syringe barrel is provided with a female threaded fitting and at the base of the strain gauge there is a corresponding threaded male fitting so that the strain gauge can be simply screwed into the female fitting to accomplish the desired attachment.
It is also customary in the art to construct the syringe apparatus from plastic materials in order to reduce the cost of the apparatus, thereby rendering the entire syringe apparatus disposable after a single procedure. On the other hand, the strain gauge device is typically a metal device and the threaded male coupling is most often fabricated from a machined brass part. On the one hand, in view of the relatively high pressures which are required to be exerted by the syringe on the contrast media, the strain gauge must be screwed into the syringe barrel tight enough to prevent leakage from occurring as the syringe is operated. On the other hand, because the female fitting on the syringe barrel is customarily plastic and the male coupling on the strain gauge is brass, screwing the strain gauge too tightly can result in cracking and breaking the female fitting. Accordingly, care must be taken in the assembly of this type of syringe apparatus not to overtighten the threaded coupling.
Another problem which is encountered when attempting to attach the strain gauge using a threaded coupling in the mentioned manner, is that it is difficult to accurately position the dial of the strain gauge while at the same time tightening the strain gauge to the necessary degree without cracking the female coupling Since typically the dial of the strain gauge must be oriented in a manner so that it can be read from a user who is grasping the syringe plunger at the proximal end of the syringe apparatus, the dial must therefore face the proximal end of the syringe apparatus so that it is readable by the user. This requirement further complicates the difficulty of properly orienting the dial when screwing the strain gauge onto the barrel of the syringe.